Sliding joint system for railway tracks, allowing a great longitudinal excursion, particularly for suspension bridges

ABSTRACT

Sliding joint system in a railway track allowing a great longitudinal excursion--particularly for suspension bridges--comprising, for each rail of the track, a first fixed rail (1) having an end tapered on the outwardly facing sides of the track, and a second rail (2) positioned next to the tapered surface of the first rail (1) and sliding along the same, while continuously extending beyond the tapered surface in an oblique direction, outwardly of the track, at an acute angle. The base flange of the second rail (2) is preferably of reduced width, equal to that of its head, so as to be more flexible. The deviation and sliding of the second rail (2) in respect of the first rail (1) are ensured by guides comprising: a first set of three guide rollers (3, 4, 5) meant to align the second rail (2) parallel to the main longitudinal axis of the track; a plurality of secondary rollers (6) with fixed vertical axes, positioned so as to face the tapered surface of the first rail (1); and pairs of coupled guide rollers (7), positioned at regular intervals along a first guide channel (8) of the second rail (2). The second rail (2) thus bends into and out of alignment with the first rail (1), upon thermal extension or contraction of the bridge, thereby to accommodate great variations in the length of the bridge whilst maintaining continuous tracks.

The present invention concerns suspension bridges comprising anessentially flat main structure, or framework, the top surface of whichforms the roadway for the transport means crossing the bridge, and asuspension system formed of catenary cables anchored to end piers of thebridge and of a plurality of vertical stays or hangers to suspend thebridge framework to the catenary cables.

As known, the longer the suspension bridge, the greater the longitudinalexcursion it undergoes, mainly due to thermal expansions, live loadvariations on the bridge, and/or displacements caused by the action ofthe wind.

The invention thus relates, in particular, to a sliding joint system forrailway tracks, allowing a great longitudinal excursion--in theory,unlimited--of one track section in respect of the other.

The problem of longitudinal excursion essentially arises incorrespondence of the end piers onto which are anchored the catenarycables to suspend the bridge, whereby sliding joints have to be providedin these areas.

As concerns the sliding joints for roadways, there are already known tobe systems allowing considerable excursions. These systems generallyconsist of parallel intersecting tracks, which are considered to providea satisfactory solution to the problem.

Whereas, as concerns railways, the only known system allowing a certainreciprocal sliding between the rails--while still ensuring a constantsupport of the train wheels--consists in tapering the opposed ends ofthe two railroad sections and placing said tapered ends side by side;the discontinuity between the two rails thus appears in the form of anoblique cut (instead of being perpendicular to the rail axis). Thenarrower the angle formed between the axis of said cut and the railaxis--i.e. the more marked the tapering--the greater the excursionallowed by such a joint system. In any case, there are no joints of thistype allowing an excursion of more than a few decimeters.

From the documents U.S. Pat. No. 2,067,598 and FR-A-2185192, joints arealso known in which only one of the adjacent ends of the rails isobliquely cut, while the other end runs close to this oblique surfaceand along the same. The advantage of this system is provided by the factthat there is always a contact between the two rails, differently fromthe above cited known technique in which the ends of the rails areseparated by an oblique slot and the width of this slot becomes greateras the ends of the rails more apart one from the other due tocontraction of the rails, i.e. owing to cooling.

Even if these known systems, as already said, have this advantages toavoid the formation of a more or less wide slot between the ends of therails, however, they do not allow wide longitudinal excursions betweenthe rails. In U.S. Pat. No. 2,067,598 (page 2, column 2, lines 23, 24)it is said that the longitudinal excursion may be of about 400 mm. andalso a less wide longitudinal excursion is foreseen in FR-A-2185192 (seethe broken lines a in FIG. 2).

In fact, all the above systems are provided for extensions andcontractions of the rails caused in particular by thermal variations.Besides in these conditions--seen from another point of view--themovements of the rails are, as known, extremely slow: normally there isonly an extension during the day and a contraction during the night.Therefore the resistance to sliding of the rails, owing to the greatfriction between them, is practically negligible.

However, in suspension bridges with a very wide span, for instance over1 Km, one should provide excursions of the order of meters. In thebridge being planned for crossing the Straits of Messina--to whichreference is made in EP-A-0.233.528, filed by the same Applicant--havinga span greater than 3 Km, the reckoned excursion is of ±3.5m in restconditions, with no traffic on the bridge. But it is perfectly knownthat, in railway technique, there is no joint system allowing anexcursion of 7 m.

Besides, in the case of a joint for a suspension bridge with a very widespan, the sliding of the rails is determined, not only by the thermicvariations, but also by the movements to which the bridge is subjectedboth owing to the load variations (which cause the flexion on thevertical plane), and to the wind action (which causes a lateral pressureand then flexions in the horizontal plane). Then these movements,besides being very wide, may happen also much more frequently and inrelatively short times, i.e. depending on the traffic and on the wind.For this reason the friction problem between one rail and the nextassumes a great importance.

The object of the present invention is therefore to propose a slidingjoint system for railway tracks, allowing a wide longitudinalexcursion--in theory unlimited, but anyhow sufficient to satisfy therequirements of modern suspension bridges--while constantly ensuring acorrect support and a precise guiding of the train wheels.

Further characteristics and advantages of the railway sliding jointaccording to the present invention will anyhow be more evident from thefollowing detailed description of a preferred embodiment thereof, givenby way of example and illustrated in the accompanying drawings, inwhich:

FIGS. 1a and 1b are diagrammatic plan and, respectively, elevation viewsof the railway sliding joint system according to the invention in anintermediate position of excursion;

FIGS. 2a and 2b are similar views in a final position of excursion;

FIGS. 3 and 4 are diagrammatic section views along the line III--IIIand, respectively, IV--IV of FIG. 1b;

FIG. 5 is a diagrammatic plan view, on an enlarged scale, of the areacomprising the sliding joint system according to the invention;

FIGS. 6 to 11 are diagrammatic section views along the lines VI--VI toXI--XI of FIG. 5.

As shown in the drawings, the railway sliding joint system according tothe present invention comprises a so-called fixed track section 1--1 anda slidable track section 2--2. FIGS. 1 and 2 show the section 1--1 asbeing integral with the embankment T, while the section 2--2 is integralwith the bridge part P-P1 which is slidable along the platforms B-B1 byway of the supports A-A1.

From the position shown in FIG. 1, the bridge end P can move in thedirection of arrow F--i.e. when subject to contraction--as far as thefinal position shown in FIG. 2, with the support A sliding alongplatform B up to reaching its outermost end. At the same time thelongitudinal beam P1, forming an extension of the bridge P, slides withits support A1 along platform B1. On the contrary, when the bridge end Pmoves in a direction opposite to arrow F--i.e. while elongation takesplace--the supports A-A1 move as far as the platform heads T1, T2.

FIGS. 3 and 4 show the tip-shaped section of the longitudinal beam P1,which slides telescopically into a guide channel B2. The slidable rail 2is fixed on the tip of the beam P1.

As shown more clearly in the plan view of FIG. 5 and in the sectionviews of FIGS. 6 to 11 (which refer to the rails 1-2 illustrated in thelower half of FIGS. 1a or 2a, but--by symmetry--also to the rails 1-2illustrated in the top half of these figures), the sliding joint systemof the present invention comprises, in a characteristic way:

on the one hand, the fixed rail 1 which is beveled, i.e. comprises avery marked tapering which practically extends between a point justbefore the section line VIII--VIII (FIG. 8 shows in fact where the bevelstarts) and a point just before the section line X--X (FIG. 10 shows infact only the rail 2, as the tapered portion of the rail 1 hasterminated);

on the other hand, the slidable rail 2, which is positioned next to thetapered portion of the rail 1, without being tapered itself (as clearlyshown in FIGS. 6 to 11), but rather bending and deviating outwardly ofthe track at an acute angle, guided along and sliding against thetapered surface of the rail 1.

Although the rail 1 has a stiffened structure (as shown in the sectionsof FIGS. 6-10), it would not be sufficient to stand the pressure forcesof the rail 2 due to its deflection. To endure this outward deflection,the rail 2 is thus constantly guided also:

by a set of three main rollers 3, 4, 5, which are also meant to alignthe rail 2 parallelly to the main longitudinal axis of the track, in aposition preceding the zone of outward deviation;

by a plurality of secondary guide rollers 6, positioned so as to facethe tapered surface of the rail 1; and finally

by pairs of guide rollers 7, positioned at regular intervals along achannel 8 meant to guide and protect the rail 2.

To be able to work correctly, the sliding joint system according to theinvention must comprise a rail 2 adapted to undergo the foreseenprogressive deflections or straightenings, while keeping within therange of its elastic limits. In other words, it is evident from theabove that the rail 2--which undergoes a certain temporarydeflection--should always be able to elastically recover its rectilinearconfiguration.

To favor said deflection, the rail 2 is preferably formed with a flangeof reduced width, for instance the same width of the head (as clearlyvisible in FIGS. 6 to 10), so as to improve the deformability by lateralelastic deflection, though allowing to keep the induced stresses withinacceptable limits, also taking into account the fatigue strength.

Reverting briefly to FIG. 1 it can be noted that, in the intermediateposition of FIG. 1a, the rail 2 extends into the channel 8 for abouthalf of its length; while in the final position of FIG. 1b, the channel8 is completely free in that the rail 2, together with the bridge P, isfully set back (maximum contraction of the bridge) whereby its end partfinds itself in contact with the rollers 6. In a fully advanced positionof the bridge (maximum elongation)--not shown in the drawings--the rail2 would occupy the whole channel 8.

It is anyhow to be understood that the invention is not limited to theparticular embodiment described heretofore, which is only a non-limitingexample of its scope, but that many other embodiments are possible--bothas to the positioning of the guide channel 8, which could be on theinner side of the track instead of being on it outer side, and above allas to the guide means of the rail 2--all these embodiments being withinreach of a technician skilled in the art and thus falling within theprotection field of the present invention.

I claim:
 1. A railway track comprising a first fixed rail having an endwhich is chamfered on an outwardly facing side of the track so as toform an oblique sliding surface, a second rail, means supporting thesecond rail for sliding movement along said oblique surface of the firstrail with a portion of said second rail in alignment with said firstrail, said second rail being a unitary body of metal having an elasticlimit, and means flexing said second rail within said elastic limit todeflect a portion of said second rail into sliding contact with saidchamfered end of said first rail while at the same time maintaining saidportion of said second rail in alignment with said first rail, whereinsaid deflecting means comprise guide rollers disposed on opposite sidesof and in rolling contact with said second rail, said guide rollershaving vertical axes.
 2. A track as claimed in claim 1, wherein saidguide rollers contact opposite sides of said portion of said secondtrack in alignment with said first track, and also a portion of saidsecond track that is out of contact with said oblique sliding surfaceand is disposed at an acute angle to said first track.
 3. A track asclaimed in claim 1, wherein said deflecting means comprise rollersrotatable about vertical axes and in contact with a portion of saidsecond rail that is in contact with said oblique sliding surface andthat is disposed on a side of said second rail opposite said obliquesliding surface.
 4. A track as claimed in claim 1, wherein said secondrail has a head and a base flange and said base flange has a width aboutequal to a width of said head.
 5. A track as claimed in claim 1, whereinsaid second rail has an end portion disposed at an acute angle to saidfirst rail, and a channel within which said end portion is disposed. 6.A track as claimed in claim 5, and guide rollers in said channel onopposite sides of and in contact with said end portion of said secondrail.
 7. A track as claimed in claim 1, said portion of said second railbeing supported by a longitudinal beam that slides telescopically in afixed guide channel disposed below said second track.
 8. A track asclaimed in claim 7, wherein said longitudinal beam and said guidechannel have sides that converge upwardly toward said second track.